Just noticed that BTT is using more memory than my browser..
That really just depends on the features you are using, and a lot of that memory will automatically clear if your system memory gets low.
For example, for window snapping BTT needs to quickly show an overlay window. Therefore these overlays are kept in memory if possible for very quick access. On retina screens basically any window (visible or cached) takes a lot of memory.
If you use a floating webview, it will require the browser engine to be loaded.
If you use the clipboard manager, it will try to keep the items quickly accessible.
There are tons of such example in BTT. It's always a tradeoff between stuff being accessible quickly and using a little bit more memory. You can try to run some app that makes your Mac run low on memory, then most apps should reduce their memory usage.
It gets even more complicated if you look at the difference between Memory, Real Memory, Private Memory and Compressed Memory (can all be accessed via Activity Monitor). I'm not sure what your screenshot is showing - best to use activity monitor directly for this stuff.
Yep, ~50MB is the base usage, then it will get more the more features you use (it will increase on-demand once the feature is used for the first time)
Got it 
Thanks Andreas!